There has been interest in development of a psychoacoustic test battery that would allow the investigator to analyze the inherent auditory distortions of the hearing impaired. This information could then be used to predict success with conventional amplification systems or to design a computerized speech processor that would modify the speech signal to compensate for observed distortions. The frequency transition in the second formant of many speech sounds is thought to be a relevant cue to consonant identification. Because of this, the difference limen (DL) for frequency has been studied as a possible component of such a test battery. Using hearing-impaired subjects, the correlation between frequency DL and word-recognition score has been weak. Several stimulus and procedural variables may have affected the measured relationship. This study will examine frequency DL for normal-hearing and hearing-impaired subjects using three brief stimuli varying in spectral complexity and speech-like quality. The stimulus conditions will include: a second formant transition alone, a second formant transition with all other formants present, and a second formant with full-formant representation plus preceding and following spectral energy, as is typical in connected speech. It is hypothesized that frequency DL will increase as the stimulus becomes more speech-like. Frequency DL will also be measured in background noise since this is the typical situation for word-recognition testing. Frequency DL has been shown to be elevated in the presence of masking in normal hearers. Consonant perception will be evaluated using naturally produced and computer-generated speech stimuli presented in background noise. The correlation between consonant identification and frequency DL in various stimuli will be examined. It is hypothesized that correlations between frequency DL and word recognition will improve when the stimulus is more representative of natural speech, if frequency DL is indeed a psychoacoustic skill basic to consonant perception.